ABOUT MAUNA LOA CARBON DIOXIDE
Data on the carbon dioxide (CO2)
content of the atmosphere at the Mauna Loa Observatory on the Big
Island of Hawaii have been measured nearly continuously since the
1950s. A portion of the data are given here, from 1974-1985. Time
is expressed in months, with May of 1974 as month 1 (zero was not
used to avoid the usual problems with exponential and power law regression).
The observatory is at 3,400 m or 11,000 feet above sea level.
The data show both a cyclic behavior and a linear trend. The cyclic behavior corresponds to a yearly cycle of
increasing atmospheric CO2 from late fall to spring, with a maximum in May, and
then decreasing atmospheric CO2 from spring to late fall, with a minimum in October.
The simple interpretation is that carbon dioxide is "scrubbed" or removed from the northern hemisphere
atmosphere during the spring-summer growing cycle, when green plants suck up CO2
during photosynthesis. Carbon dioxide is then released during fall and winter, when plants die and rot.
The linear increase of mean yearly atmospheric CO2
with time is actually an exponential increase of mean yearly atmospheric
CO2 as measured over a longer time
scale beginning in the late 1950s. The yearly increase appears linear because
of the short time scale selected for this data set. Fossil fuel consumption appears to be the prime source of
this secular increase, with occasional oceanic contributions due to
changes in sea surface temperatures associated with currents like
El Nino. To see the lastest long-term data, including interpolations for missing values, go to DataSet
Students could find the linear regression for this data set, then subtract that linear increase from
the actual data to isolate the cyclic behavior. The cyclic data could then be modelled with simple sinusoidal functions.
Notice that there is a "knee" in every yearly cycle from January to December when carbon dioxide concentration
does not increase as fast as one might expect. The residuals from the sinusoidal model might prove interesting.
Reference: Komhyr, W. D., Harris, T. B., Waterman, L. S., Chin, J. F. S. and Thoning, K. W. (1989), Atmospheric
carbon dioxide at Mauna Loa Observatory 1. NOAA Global monitoring for climatic change measurements with a nondispersive
infrared analyzer, 1974-1985; J. Geop. Res., v. 94, no. D6, pp. 8533-8547.
Thoning et al (1989), "2"; JGR v. 94, pp.
Keeling et al (1976), Tellus v. 28, pp. 538-551.
Martin and Diaz (1991), JGR v. 96, pp. 18689-18704.
Rust etal (1979), JGR v. 84, pp. 3115-3122,